Soil Thermal Conductivity Affected By Salt Solutions.

Clay is often used as the most outer layer of permanent disposal sites for industrial wastes including radioactive materials. Those sites are sometimes built near coastal areas where groundwater contains seawater. In irrigated agriculture, soil containing a clay fraction is often affected by soluble salts of the irrigation water. Under natural conditions, water flow in those soils may be affected by heat flow regulated by thermal properties. Thermal properties are known as functions of water content, temperature, texture, structure, and salt concentration. Effects of water content, temperature, texture, and salt concetration have been well studied whereas those of structure altered by salt concentration have had little attention so far. Thermal properties, i.e. thermal diffusivity, volumetric heat capacity, and thermal conductivity, of clay-containing soils affected by salt concentrations were investigated using the dual-probe heat-pulse method. As concentrations of NaCl and CaCl₂ increased from 0 to 1.0 mol/L in unsaturated loamy sand, loam with montmorillonite or kaolinite, and volcanic ash soil with various water content ranged between 0.1 and 0.3 m³/m³, thermal properties of those soils decreased as reported by previous studies. There were big dips in decreasing thermal properties of the soils toward 0.05 mol/L either NaCl or CaCl₂. Altered micro-structures of clay, silt, and sand particles by salt solutions might contribute to those large decreases in thermal properties.